Vaguely aware that Vitamin D is one of those things you should be conscious of but unsure why and how much you should taking... if any? Then read on.

So what is it and why is it important?

Put simply, Vitamin D is pretty vital to good health. We create it ourselves when our skin is exposed to sunlight of sufficient strength. Very small amounts are also found in certain foods, but not really enough to be of practical benefit. It's commonly thought that eggs and milk can be a good source of Vit D, but in reality we would have to eat 143 large eggs or drink 6.25L of whole milk PER DAY to achieve a meaningful dose! I mean, I love my eggs but...

Vitamin D deficiency is a growing problem (Holick and Chen, 2008), partly due to our increasingly indoor lifestyles and use of sunscreen as a way of preventing skin cancer. Unfortunately this can result in many health complications, both for adults and children. These can include:

For Children

• A slower than normal growth pattern
• The onset of rickets

For Adults

• An increase in the risk of osteoporosis and will worsen it if already present
• An increase in the risk of bone fractures
• The weakening of muscle
• An increase in the risk of falling
• Bone and joint discomfort and pain (often then misdiagnosed as fibromyalgia, arthritis, chronic fatigue or similar diseases)

What are the proven benefits?

So on the flipside, what kind of benefits will we see if we are able to achieve optimal levels of Vitamin D... and what are optimal levels anyway?

First things first, optimal levels are as ever an estimate. But it is currently thought that in order to avoid being deficient we need to have blood concentration levels above 50 nmol/L (20 ng/mL for US readers), with optimal levels being around 75-100 nmol/L (30-40 ng/mL). Vitamin D poisoning (yes, it's a thing!) takes place at levels above 375 nmol/L (150 ng/mL) (Holick and Chen, 2008). Obviously to find out your own levels, you will need to have a blood test.

On to those benefits then...

• Boosts immunity and reduces the risk of developing upper respiratory tract infections (colds and flu) (Martineau et al, 2017)
• Improves bone health by supporting calcium absorption (Hill et al, 2013)
• Reduces depressive symptoms (Shaffer et al, 2014) 
• Potentially improves strength (Tomlinson et al, 2015)
• Potentially aids fat loss (Ortega et al, 2008)

Anything else?

Just on that last point, Carrillo et al (2013) recently found that Vitamin D supplementation, when combined with a 12 week resistance training programme in overweight and obese participants, seemed to result in a greater improvement in waist to hip ratio. This can be seen in the diagram below (25OHD is the chemical term for circulating vitamin D) .

Basically, the waistline of those supplementing with Vitamin D reduced at a faster rate than those who weren't supplementing. A big plus for most people looking to lose weight! There seems to be a positive effect in improving body composition.

Other Considerations

It shouldn't be forgotten that circulating vitamin D is affected by skin colour. Essentially those with fairer skin are more efficient at making it through contact with sunlight. Therefore those with African or Middle Eastern ancestry are more likely to need a higher level of supplementation in order to get to that optimal, beneficial level (Hall et al., 2009). 

The take-away

• Vitamin D is definitely something you should be considering supplementing with, especially if you live in a northerly latitude or spend a lot of your time indoors.
• Optimal, personalised dosage can be found through a simple blood test.
• In general, a continuous supplementation for adults of around 2000iu in the summer and between 2500 and 4000iu in winter can be seen as a safe and potentially effective dose.
• It is a fat-soluble vitamin and therefore is best absorbed when taken alongside fat. A glass of whole milk or some yoghurt would be ideal.
• Vitamin D poisoning is a possibility under excessive dosages. This can have very serious medical consequences, therefore it is recommended to stay within safe levels and if possible attain a blood test.